By Dr. Scott H. Froum, Academy News Editorial Consultant
Dental implantology has become one of the most widely accepted methods of tooth replacement for hopeless and missing natural teeth. Although the literature has shown that this option for tooth replacement is highly predictable, with high survival rates, complications do occur. One of the more serious complications that can occur is alteration of sensation after implants are placed in the posterior mandible. Altered sensation occurs as a result of injury to the inferior alveolar (IAN) or lingual nerves due to a variety of factors, such as trauma from local anesthetic injections, implant osteotomies, and/or impingement of the dental implant into the IAN space. Prevalence of these complications has been reported to be as high as 13%.

To block or not to block: placing implants in the posterior mandible

Depending on the extent of injury to the nerve bundle altered sensation can vary from mild, transient, dysesthesia, to complete anesthesia of the affected area. Because of the clinical and legal implications of paresthesia induced by implant therapy, many safeguards have been created in order to preclude nerve injury. Stop drills, surgical guides, cone beam computer tomography (CBCT) tracing, guided satellite imaging, and changing anesthetic technique have all been advocated as methods to avoid trauma to the IAN. This article will discuss the rationale, efficacy and practicality of using mandibular infiltration as an alternative to block anesthesia prior to posterior implant placement.

Three major postoperative issues can occur when using block anesthesia prior to placing implants in the posterior mandible. Toxicity of the local anesthetic solution can occur, if injected mistakenly into the artery. Because soft tissues remain anesthetized longer compared with mandibular infiltration, patients undergoing block anesthesia can have self-inflicted, macerating wounds to the tongue and lip. Lastly, injury to the mental nerve and IAN can physically occur by encroachment of the osteotomy drills and/or dental implant during placement.

Although there is no consensus, the idea has been proposed in the literature that by substituting mandibular infiltration anesthetic for block administration, the patient will still have enough sensation to determine when the implant armamentarium is close to the nerve and therefore able to give feedback to help prevent nerve damage. In a 2001 retrospective analysis, Heller et al looked at 8,000 implant cases placed in the posterior mandible over a 32-year period in private practice. They used 1 carpule (1.8ml) of 2% lidocaine deposited into the lingual tissues and 1 carpule deposited into the buccal tissues prior to implant therapy. They used standardized periapical radiographs to determine the location of the IAN canal and mental nerve.

Their results showed that of 8,000 implants placed under mandibular infiltration, only 3 patients experienced permanent paresthesia. The affected areas were 15×15 mm in diameter on the lower lip, and all three patients reported feeling a pin prick on the buccal surfaces. Heller claimed that “none of the three patients feel the anesthetized area is objectionable nor does the loss of sensation alter their routine of daily living.” In addition, Heller reported that 85-100 patients had transient paresthesia lasting 3-6 months, which typically dissipated 3-4 weeks after surgery. Heller concluded that mandibular infiltration was a safe and effective way to place dental implants that still allows the patient to have enough sensation to alert the surgeon when the implants were in close proximity to the nerve bundle. He suggested that mandibular infiltration replace block anesthesia when placing implants in the posterior mandible.

In a similar study in 2011, Etoz et al placed 52 implants in the posterior mandible (posterior to the mental nerve) of 29 patients using 2 carpules of articaine to anesthetize the buccal and lingual tissues. Only 2 patients required additional nerve block anesthesia due to pain during implant placement. Both patients had implants placed in the second mandibular molar sites. Once again, the location of the IAN canal was determined by standardized periapical radiographs and none of the patients in the study experienced paresthesia.

An important point to note from these studies, as well as other, older studies where mandibular infiltration was used when placing posterior mandibular implants, is the use of periapical radiography instead of CBCT as a means on IAN identification. In the time since the Heller and Etoz studies were published, radiographic technology has improved greatly. From CBCTs, we now know variations exist in the path taken by the IAN. Improved three-dimensional imaging has shown variations in the anterior loo can occur between 7-88% of the time, with a mean prevalence of 28%. In addition, up to 40% of the main IAN canal can have accessory branches. If these branches are large enough, they can form two (bifid) or even three (trifid) canals. These anatomic variations are often difficult to discern on standard two-dimensional radiographs.

Many clinicians argue that in the era where CBCT should be used as a ‘standard of care’ method to detect the IAN canal, block anesthesia is the best option when placing implants in the posterior mandible. From a patient management perspective, having a totally pain-free implant experience, while not having to stop the procedure to further anesthetize, is desirable for both patient and clinician. Block anesthesia, many would argue, is a more predictable technique for achieving that goal as compared with mandibular infiltration.

According to Dr. Geoffrey Bauman, a periodontist in private practice, who relies on CBCT as an accurate method of detecting the IAN:

I’ve been doing implants for 27 years. The first six of those I blocked the IAN for mandibular implants in the posterior. Then I took an externship in which we were taught to just take care of the long buccal and lingual and that provides a “back-up safety margin” by leaving the IAN sensate. If you’re bumping up against the IAN, the patient will feel it. I have the utmost respect for my externship trainers and did that for a while. But occasionally, I would get shock-like sensitivity and be 2-4 mm away from the IAN based on radiographic findings. Of course, when that happens, then I have a decision to make: do I place the implant at that depth if possible, abort, or ignore and press on. After a couple of years, I just went back to blocking the IAN because when I didn’t and the patient felt me working, I started just blocking the IAN and proceeding. When I just blocked the IAN ahead of time it was never a problem. I’ve never, in 27 years, had any IAN pathosis afterwards. Every once in a while, I decide to “play it safe.” But it is so frustrating to get in the middle of the procedure and have to advise the patient and then either abort of block and press on.

A second important point to note is that many studies show that infiltration with 4% articaine is equivalent to 2% lidocaine block anesthesia as it relates to the profoundness of tissue anesthesia. Because of articaine’s pKa value, its ability to penetrate bone tissue upon infiltration is superior to lidocaine. Because of this equivalency, clinicians should be careful not to have a false sense of security when infiltrating the posterior mandible with articaine for implant placement, because it may be similar to blocking the area with lidocaine.

In conclusion, many studies that advocated the use of mandibular infiltration instead of block anesthesia for the purposed of posterior implant placement did not utilize CBCT for nerve detection. In addition, studies suggest that, despite being 3-6mm away from the IAN canal (as determined by periapical radiography), patients are still able to feel sensation following mandibular infiltration and require subsequent nerve block. This scenario is especially true in the mandibular second molar region. Although periapical radiographs and mandibular infiltration may have been an historical method of nerve trauma prevention, modern technology allows us to be much more accurate. Because CBCT radiographs are easy to obtain, any question about the location of the IAN or mental nerves can now be easily answered.

References are available on the PDF version of the article. CLICK HERE to view.